Method of preparing cellulose propionate isobutyrate



United States Patefifi NIETHOD OF PREPARING CELLULOSE PROPIONATE ISOBUTYRATE Carl Malm and Loring Blanchard Rochester thereof with watersuchvas by soaking the cellulose in water and removing the. .water withan organic acid such N. Y., assignors to Eastman Kodak Company,Rochester, N. Y., a corporation of New Jersey No Drawing. ApplicationNovember 18, 19.54 Serial No. 469,830 r r 1 Claim. (Cl. 260,-225) Thisinvention relates to cellulose propionate isobutyrates'and theirpreparation; ,1

Of the lower fatty acid esters of cellulose, cellulose acetate isprobably the most commonly known. This cellulose ester, however, is'notsoluble in many' organic solvents and the products obtained Etherefromlexhibitl a comparatively 'low moisture resistance. "In thosecases wheregood solubility and/or high moisture resistance are of importance,cellulose acetate-butyrates are usually employed. These esters, however,have been characterized by an odor such as would result from traces ofbutyric acid which might be liberated at high temperatures or under longstoring conditions or as a result of standing in contact with a dead airspace for some time. To avoid this odor efiect cellulose acetateisobutyrates have been prepared but esters of this type having an evendistribution of acetyl and isobutyryl groups throughout the celluloseester are diflicult to prepare due to the wide difference in activitybetween acetic and isobutyric anhydrides. In some cases with theseesters even distribution of the acyl may not be a serious disadvantagebut in other cases such as in using borderline solvents or solventcombinations therefor or Where high molecular weight plasticizers areemployed even distribution is very important. Thus in the plasticsindustry or in the manufacture of lacquers even distribution of the acylgroups in the cellulose acetate-isobutyrates is often desirable.

One object of our invention is to provide cellulose esters of highmoisture resistance and freedom from odor in which even distribution ofthe acyl therein is not essential. Another object of our invention is toprovide esters the manufacture of which is free of the difiicultiesencountered where the preparation of uniform products is essential.Another object of our invention is to provide a method of preparingcellulose esters characterized by high moisture resistance, goodsolubility properties and freedom from odor. Other objects of ourinvention will appear herein.

We have found that if isobutyric acid esters of cellulose are preparedin which propionyl is employed as the secondary acyl, products areobtained having highly desirable properties and with propionyl ratherthan acetyl it is less important that the acyl groups are uniformlydistributed therethrough due to the better solubility of propionatescompared to acetates. We have found that the lower reactivity ofpropionic anhydride and come quently the smaller spread of activitybetween propionic and isobutyric anhydrides tends to result in a productof more uniform properties than is obtainable when the highly reactiveacetyl groups are used in the mixture in which isobutyric acid esters ofcellulose are prepared. We have found that esters of high viscosity aremuch more easily obtained in the case of cellulose propionateisobutyrates due to the greater solubility of those esters in theesterification mixture as compared to the cellulose acetateisobutyrates.

In its broadest aspects our invention comprises the cellulose propionateisobutyrates having an isobutyryl content of at least and the method ofpreparing those esters by reacting upon cellulosewith a mixture ofisobutyric anhydride and propionic anhydride oracidi- In the making ofcellulose propionate isobutyrates bya process in accordance with ourinvention, it is desirable that the cellulose be first activated byswelling the fibers as acetic acid and ,then with isobutyric acid orpropionic acid orby activating the cellulose by treating it with aqueoussulfuric acid, such as of 5-10% concentration.

' i The activation of cellulose may be" carried out convenorisobutyricacidor by isobutyric orpropionic acid-directly or thecellulose may be activated by soaking'it in aqueous v sulfuric aciclfollowed by centrifuging and then removing thewa'ter from the cellulosewith propionic acid, or a mixture of propionic and isobutyric acid. Thepreparation of cellulose for esterification by treatment with aqueoussulfuric acid is described in our application Serial No. 469,833, filedof even date.

The esters in accordance with our invention are those in which the onlyacyl groups employed to esterify the cellulose are isobutyryl andpropionyl groups with at least 50% of the acyl thereon being isobutyryl.These esters are readily soluble in. various organic solvents and alsoare susceptible to plasticization by a wide range of plasticizers so asto form plastic products having excellent properties. These esters maybe either substantially completely esterified or if desired they may besubjected to partial hydrolysis.

The following examples illustrate our invention:

Example 1 Cellulose was activated by immersion in distilled water at F.The water was centrifuged from the cellulose which was then dehydratedwith acetic acid and the acetic acid removed with isobutyric acid. Afterthe centrifuging was terminated there resulted a 6.8 lb. cake consistingof approximately 3.5 lbs. of cellulose and 3.3 lbs. of isobutyric acid.This cake was mixed in a Werner-Pfleiderer mixer with a mixture of 10.5lbs. of isobutyric anhydride, 2.9 lbs. of propionic anhydride and 1.75lbs. of zinc chloride. The reaction was carried out at 120-135 F. After5V2 hours the cellulose had been completely esterified whereupon amixture of 2 lbs. of distilled water and 8 lbs. of acetic acid was addedthereto and after incorporation of this addition there was then added amixture of 3.5 lbs. of distilled water, 16.5 lbs. of acetic acid and cc.of concentrated hydrochloric acid. The mass was held at 100 F. for 24hours whereby the ester was partially hydrolyzed whereupon it wasprecipitated from the mass and Washed with distilled water. A cellulosepropionate isobutyrate was obtained having an intrinsic viscosity inacetic acid of 2.0.

Example 2 4.2 lbs. of esterification type cotton linters were soaked in70 lbs. of 10% aqueous sulfuric acid for 5 minutes at 60 F. Thecellulose mass was then centrifuged and was given four 5 minute changeswith 12 lbs. of a mixture of equal parts of propionic and isobutyricacids at 60 F., the cellulose being centrifuged between each change. Acellulose cake was obtained approximately consisting of 4 lbs. ofcellulose, 1.8 lbs. propionic acid, 1.8 lbs. isobutyric acid and 100grams of sulfuric acid.

This cellulose cake was added to a Werner-Pfleidcter Pa e Mar. .25, lossmixer containing 15 lbs. of isobutyric anhydride and 1.65 lbs. ofpropionic anhydride and was run at a temperature of 7280 F. for 5 /2hours whereby a solution was obtained free 'of fibers. The cellulosepropionate Visobutyrat e obtained was precipitated fromthe mass. Itwasof variouslcinds.

foundtorbe useful for the preparationof plastic-products- Humble '0;81b.. of esterificati'on a grade cellulose-was soaked in 1 .5 .lbs, of-15% aqueous sulfurio 'acid for 5 minutes at 60 The cellulose was thencentrifuged for L minute an'diwassgilven 4 changes offi minuteseach-with 2&5 =-lbs1 ofipropionic'iacid at 60 F. Ihe eellulosewascentrifuged between ea'chdclran'ge. The cake-fobtainedi weighed 1.6 lbs.and "contained 19191 grams;of -su1uric acid; This cellulosewaslint'rodu'ced info W'erner Pfieid'erer mixer containirrgBA lbs; erisobutyrie anhydridea d "was run at 68-80 After 7' hours a unifo'r mmas's-tfree of fibers was obtained. The cellulds'e propionatmisobutyratethus obtained was precipitated fro m the' masswith'distflledwater. f Aproduct having goodplastic properties was obtained.

We claim: 7 V l A method of preparing a cellulose propionate isobutyratehaving good solubility properties and high moisture resistance whichcomprises swelling cellulose with water, removing the water from thecellulose by acid displacement whereby a mass consisting ofapproximately 1 part each of cellulose and isobutyric acid is obtained,mixing the mass with approximately 3 parts oi isobutyric anhydride,. andapproximately 0.8 part of propionilc anhydride and approximately 0.5part of zinc chloride catalyst, substantially all of the acyl beingpropionyl and'iso'butyryl, and continuing the mixing underestetificatiori conditions until thecellulose'hasbeen substantiallyesterified. 1 t

References Cited the file of 'this patent UNITED STATES PATENTS2,478,396 Hi'ncke' et al. June 27, I945

